Research And Development Of PH Spline Curves Parallel Interpolation And CNC System Based On The Signal-Chip Multi-core Microprocessor

The NURBS (Non-Uniform Rational B-Spline) curve technology has been very mature in the CAD applications. But, in the NC machining, a lot of real-time calculations about arc length and tool radius offset make the NURBS interpolation computationally intensive, time-consuming, difficulty to ensure accuracy, that limits its wide range of applications. The appearance of the PH curve can completely change the situation.Combining the multi-core single-chip’s parallel processing advantages with the distinguishing feature of Pythagorean-Hodograph (PH) curve in the NC machining, we put forward the idea of developing a CNC system with PH spline curve interpolation function based on multi-core microcontroller.First, the definition of PH curve is introduced, and then the calculation expressions of PH curve’s arc length and its offset curves is given. From the expressions we can see that the arc length and offset curves of PH curve can be accurately calculated. Then the structure and properties of genaral cubic and quintic PH curve are introduced.The Parallax’s multi-core microcontroller P8X32A-D40 is selected as hardware platform of CNC system, based on parallel pipelined architecture of software, the tasks of related cores are assigned, an overall architecture of the PH curve CNC system is proposed.Then the system hardware test platform is set up, which includes the peripheral circuits of muti-core microcontroller, the input and output operation circuits and the stepper motor drive circuit.Next, the software design and development of main core module and other related core modules are completed, which include modules of CRT display, PS/2, and related functions software, the NC decoding module, parameter calculation module, coordinate calculation module, motion control module under the condition of PH curve constant speed feeding, stepper motor drivers module etc.Finally, the system operation and performance test are carried out. The main bottleneck which affects the speed of interpolation is analyzed. The experiment results show that:the speed of parallel interpolation scheme realized in this paper is increased by about 75% than general serial interpolation scheme, and the system is reliable, high precision, low cost. The desired purpose is achieved.Above research work gives out a beneficial attempt at taking multi-core microcontroller as the control unit of the numerical control system. It has a certain theoretical value and reference value at trying to develop high-speed, high-precision spline curve CNC system.